1. Field of the Invention
The present invention relates to a method for operating a storage system comprising a main site and a back-up site.
2. Description of the Related Art
A storage system provides large-capacity and high-performance storage services to a host computer (business server, and the like). In a storage system, for example, a storage region is constituted on the basis of a RAID (Redundant Array of Independent Inexpensive Disks), formed by providing a plurality of disk drives in an array configuration. Logical volumes (LU: Logical Units), which are logical storage regions, are formed in the physical storage regions provided by the respective disk drives. A host computer is able to read and write data from and to these logical volumes.
The storage system stores and manages a large volume of data groups of various types which are used in a variety of organizations, such as businesses, autonomous bodies, universities, and the like, for example. In many cases, these data groups are absolutely indispensable to the activities of the organization. Therefore, various countermeasures are adopted in a multi-layered fashion in the storage system, in order to prevent the loss of important data groups, or situations where data groups become unusable.
For example, redundancy is created in the physical configuration and logical configuration of the storage system, by adopting an alternative path structure or a RAID structure, or the like, in order to prepare for the occurrence of faults, or the like. Furthermore, in a storage system, it is possible to back up the storage contents of the logical volumes, to a back-up device, such as a tape device, or the like, at regular or irregular intervals.
Furthermore, in a storage system, in order to prepare against large-scale disasters, such as earthquakes, or the like, for example, a back-up site can be situated in a location that is distant from the main site, in what is known as a “disaster recovery” system. Disk array devices for backing up data are located in this back-up site, and the storage contents thereof are synchronized with those of the disk array devices in the main site.
Remote copy technology is used in order to synchronize the storage contents in the main site and the back-up site. In a remote copy system, the respective disk array devices are mutually connected by means of a dedicated communications circuit or a public circuit, and the data is copied directly between the respective disk array devices, without passing via a host computer (see Japanese Patent Laid-open No. 2002-7304).
Furthermore, for example, a method is also known whereby the storage contents of the disk array device in the main site are backed up to magnetic tape, which is taken to the back-up site, and then restored onto the disk array device of the back-up site.
Moreover, technology is also known whereby disk drives are replaced in a frame, or moved to a different frame (Japanese Patent Laid-open No. 2001-337792).
When the storage contents of the main site are to be copied to a back-up site, firstly, an initial copy is made (establish copy), and the storage contents of the main site at a particular point in time are copied exactly to the back-up site. Thereupon, the data updated in the main site is transferred to the back-up site, as differential data, and is copied to a storage region of the back-up site.
In a method wherein the initial copy is carried out via a communications circuit, although the situation may vary depending on the bandwidth and speed of the communications circuit, and the volume of the data to be copied, and the like, in general, a long time is required in order to make the initial copy. Therefore, it takes time for the back-up site to start up. Furthermore, if the communications circuit is occupied for the purposes of making the initial copy, then this may affect other types of data communications using the same communications circuit.
In a method whereby the data at the main site is backed up onto magnetic tape and then taken to the back-up site, no communications circuit is required. However, in general, the data write speed and data read out speed of a tape device is slower than that of other storage devices, and hence a long time is required in order to start up the back-up site. Since magnetic tape, which has a slow access speed, is used for both writing the data from the main site and reading out data into the back-up site, then it takes time to construct the back-up site. Furthermore, the magnetic tape device used for back-up is a control device that is completely independent from the disk array device. Consequently, if data back up based on the use of magnetic tape is to be adopted, then a magnetic tape device must be purchased.
In the reference patents described above, a method is disclosed wherein disk drives are moved to different frames. However, this reference patent simply discloses a method for moving an original disk drive to another frame, and it does not consider the construction of a back-up site for the purpose of disaster recovery.